Melt butter in sauce pan over medium-low heat. Remove from heat, add chips, and stir until melted. Set aside to cool for 5 minutes.

Lightly beat the egg in a medium bowl. Stir in the brown sugar, banana, vanilla, and salt. Pour the melted chocolate mixture into the banana mixture, and stir until well combined. Add the flour, stirring just until incorporated. Spread the batter into the prepared pan.

Bake in the preheated oven until a toothpick inserted near the center comes out with moist crumbs, about 30 minutes. Don't over bake. Remove, and cool pan on wire rack before cutting.